Conventionally, as a drawing system for performing the drawing of cylindrical members such as pipe tips, etc., a working system is attempted which consists of slidably supporting a drawing tool in a radial direction on a drawing tool mounting base attached to the tip of the turning spindle, and thereby performing the drawing work.
In such a case, as a means of moving the drawing tool supported on the drawing tool mounting base in a radial direction, a structure is adopted in which a cam plate is provided for moving the drawing tool in a radial direction on the drawing tool mounting base. The mounting base is attached to the tip of the spindle, while, on the other hand, the cam plate is attached to the tip of the cam shaft in which to insert the spindle. The cam shaft transmits rotation from the spindle through a differential gear mechanism.
In addition, a differential gear mechanism is generally constructed by using a planetary system as disclosed in JP, 3-8412, B, for example, in which a plurality of planetary gear mechanisms are connected in series with the spindle and the cam shaft. The spindle and cam shaft turn at the same rotating speed for normal work, while the rotating speed of the cam shaft is changed, with the use of planetary gear mechanisms, when moving the drawing tool in the radial direction.
However, a mechanism of this construction had various problems, such as the necessity of having a large number of component parts, a problem with durability due to the complicated structure and the necessity of constantly turning the planetary gears at high speed, poor accuracy in the final casting shape due to the fact that a mandrel inserted in the raw material forms an integral body with the spindle and turns, advances and retreats together with the spindle, etc.
Moreover, while it is desirable, to secure final shape accuracy at the reduced diameter parts of casting, to make the tip of the mandrel protrude near the roller by passing and holding the mandrel through the spindle, there was also a problem of it being impossible to pass and hold the mandrel through the spindle, because two sets of large and heavy planetary gear mechanism are inserted in the auxiliary shaft and there is no way to produce a hollow state in the auxiliary shaft and a spindle there.